Heretofore, radiation images such as X-ray images have widely been employed in hospitals and clinics for the state of a disease. Specifically, over a long period of history, radiation images formed via intensifying screen-film systems have resulted in high photographic speed and high image quality, whereby even now, they are employed in hospitals and clinics in the world as imaging systems which simultaneously exhibit high reliability and cost performance. However, types of the above image information are those of so-called analogue image information, and enable to achieve neither free image processing nor instantaneous electric transmission, which are realized in digital image information which have been developed in recent years.
Further, in recent years, digital system radiation image detectors, represented by computed radiography (CR) and flat-panel type radiation detectors (FPD) have appeared. These enable direct formation of digital radiation images and direct display images on image display devices such as a cathode tube or a liquid crystal panel can be achieved. When applying these radiographies, images are not always required to be formed on photographic film. As a result, the above digital system X-ray image detectors have decreased the need of image formation via silver halide photographic systems and have significantly enhanced convenience of diagnostic operation in hospitals and clinics.
As one of the digital technologies of X-ray images, computed radiography (CR) is presently employed in medical settings. However, sharpness is insufficient and spatial resolution is also insufficient, whereby its image quality level has not reached that of the screen-film systems. Further developed as a new digital X-ray image technology are flat-panel X-ray detectors (FPD) employing thin-film transistors (TFT), which are described, for example, on page 24 of John Rawland's report, “Amorphous Semiconductor Usher in Digital X-ray Imaging”, Physics Today, November 1997 and on page 2 of L. E. Antonku's report, “Development of a High Resolution, Active Matrix, Flat-panel Imager with Enhanced Fill Factor” of the magazine of SPIE, Volume 32, 1997.
In order to convert radiation to visible light, employed are scintillator panels which are prepared employing X-ray phosphors exhibiting characteristics of emitting light via radiation. However, in order to enhance the SN ratio during imaging at low dosages, it becomes necessary to employ scintillator panel at a high light emitting efficiency. Generally, the light emitting efficiency of scintillator panels is determined by the thickness of the scintillator layer (also called a “phosphor layer”) and the X-ray absorption coefficient, while as the thickness of the scintillator layer increases, scattering within the scintillator layer of emitted light occurs, which lowers sharpness. Consequently, when required sharpness for image quality is determined, the layer thickness is determined.
Of the above phosphors, cesium iodide (CsI) exhibits a relatively high conversion ratio from X-rays to visible light and it is possible that phosphors are easily formed in a columnar crystal structure via vapor deposition. Consequently, scattering of emitted light in crystals is retarded via optical guide effects, whereby it has been possible to increase the thickness of the scintillator layer.
However, when only CsI is employed, the light emission efficiency is relatively low. Therefore, as described for example, in Japanese Patent Publication No. 54-35060, a mixture of CsI and sodium iodide (NaI) at any appropriate mol ratio is deposited on a substrate in the form of sodium-activated cesium iodide (CsI: Na), employing vapor deposition, and recently a mixture of CsI and thallium iodide (TlI) at any appropriate mol ratio is deposited on a substrate in the form of thallium-activated cesium iodide, employing vapor deposition. The resulting deposition is subjected to annealing (a thermal treatment) as a post-process to enhance the visible light conversion efficiency, whereby resulting materials are employed as an X-ray phosphor.
Further proposed as another means to increase light output are a method in which a substrate which forms a scintillator is made to be reflective (refer, for example, to Patent Document 1), a method in which a reflective layer is arranged on the substrate, and a method in which a reflective thin-metal film arranged on the substrate and a scintillator on the transparent organic film covering the metal thin-film are formed (refer, for example, to Patent Document 2). These methods increase the resulting light amount, while problems occur in which the sharpness is significantly degraded.
Still further, methods to arrange a scintillator panel on the surface of a flat light receiving element are described, for example in JP-A Nos. 5-312961 and 6-331749. However, these methods result in poor production efficiency, and degradation of sharpness on the scintillator panel and the flat light receiving element surface is unavoidable.
Heretofore, it has been common that as a production method of scintillators via a gas layer method, a scintillator layer is formed on a stiff substrate and the entire surface of the scintillator is covered with a protective film (refer, for example, to Patent Document 3). However, when the scintillator layer is formed on such a substrate, which is not easily bent, drawbacks result in which, during adhesion of the scintillator panel onto the surface of the flat light receiving element, uniform image quality characteristics are not realized in the light receiving plane of flat-panel detectors due to effects such as deformation of the substrate or curling during vapor deposition. Further, when the substrate is composed of metal, X-ray absorption increases, whereby in terms of realization of lower X-ray exposure, problems have occurred. On the other hand, amorphous carbons, which have recently been employed, are useful in terms of less X-ray absorption. However, since universal products of a large size are unavailable and the price is very high, it is difficult to state that they are suitable for practical production. Accordingly, in recent years such problems have risen along with the increase in size of flat-panel detectors.
In order to avoid such problems, commonly employed are a method in which a scintillator is formed directly onto the surface of a flat light receiving element (on the imaging element) via vapor deposition, and a method in which a scintillator panel such as a flexible medical intensifying screen is employed as a substitute. Further, an example is disclosed in which a flexible protective layer such as poly(para-xylylene) is employed (refer, for example, to Patent Document 4).
Scintillator materials directly vapor-deposited onto the flat light receiving element exhibit highly desirable image characteristics. However, a drawback in terms of cost occurs in such a manner that when vapor-deposited products are unacceptable, expensive light receiving elements are wasted. Another drawback is that even though image desirable characteristics of scintillator materials are enhanced via a thermal process, the processing temperature is limited due to the fact that light receiving elements are weak for heat. Further, a problem occurs in which complexities result in such a manner that it is necessary to incorporate cooling of light receiving elements in the above thermal process.
Accordingly, in order to overcome problems as described above, it has been increasingly demanded to develop a radiation flat-panel detector which exhibits excellent production adaptability, minimizes deterioration of characteristics during aging, protects the scintillator (namely the phosphor) layer from chemical modification or physical impact, results in minimal degradation of sharpness between the scintillator panel and the surface of the flat light receiving element, and results in desired characteristics of uniform image quality.
(Patent Document 1) Japanese Patent Publication No. 7-21560 (WO 92/06476)
(Patent Documents 2) Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 2000-356679
(Patent Document 3) Japanese Patent No. 3566926 (WO 99/066345)
(Patent Document 4) JP-A No. 2002-116258
In view of the foregoing, the present invention was achieved. An object of the present invention is to provide a scintillator panel which exhibits excellent suitability for production, high efficiency to draw light emitted by a scintillator, high sharpness, and minimal degradation of sharpness between the surfaces of flat light receiving elements, and a flat-panel radiation detector using the same.
An object of the present invention can be achieved by the following embodiments.
1. A scintillator panel comprising a scintillator plate comprising a substrate having thereon a reflective layer, a sublayer and a scintillator layer in that order,
wherein the scintillator plate is sealed with:
a first protective film provided on a side of the scintillator layer; and
a second protective film provided on a side of the substrate opposite the scintillator layer,
wherein the first protective layer is not adhered to the scintillator layer, and the second protective layer contains an aluminum layer.
2. The scintillator panel of the above-described item 1,
wherein the scintillator layer is a columnar phosphor layer comprising cesium iodide, and the scintillator layer is produced by a gas phase deposition method.
3. The scintillator panel of the above-described items 1 or 2,
wherein the substrate is made of a heat resisting resin.
4. A flat-panel radiation detector comprising:
the scintillator panel of any one of the above-described items 1-3; and
a flat light receiving element,
wherein the scintillator plate is arranged facing the flat light receiving element without physicochemical adhesion to a surface of the flat light receiving element.
By the above means of the present invention, it is possible to provide a scintillator panel which exhibits excellent production suitability, high efficiency to draw light emitted by a scintillator, high sharpness, and minimal degradation of the sharpness between the surfaces of flat light receiving elements, and a flat-panel radiation detector using the same.